Noncovalently Functionalized Halloysite Nanotubes for Use in Reinforced Polymer Composites

The inorganic halloysite nanotube (HNT) is a promising type of naturally occurring fillers with many important uses in different fields. An HNT has a relatively low content of hydroxyl groups on its surface, which makes it relatively hydrophobic, although this is not always sufficient to guarantee good interfacial adhesion in composite systems. Further surface treatment is required to improve the compatibility of HNTs with polymer matrixes, maximizing interfacial interactions. The aim of the present work was to study a noncovalent functionalization of halloysite with 2,2′-(1,2-ethenediyldi-4,1-phenylene) bisbenzoxazole (EPB), based on electron transfer, for further use of EPB as a coupling agent in polymer/HNT compatibility. A set of characterization techniques were performed to evaluate the chemical and physical properties and evidence the functionalization. The results revealed the surface modification of halloysite upon functionalization. Emphasis was for powder wettability by tensiometry based on Washburn because no studies about halloysite powders using this technique could be found in the literature. The results demonstrate a reduction in the total surface energy of the system, usually accompanied by a reduction in the polar component upon HNT modification.